Metagenomic analysis of the skin microbiome
Human skin represents a diverse population of microorganisms. This population varies depending on location on the body and factors from the environment. Human immune systems provide innate and adaptive immune responses that affect the skin microenvironment. Metagenomic studies are useful for identifying microbial communities that reside on the skin, and how these communities change in skin disorder cases. Microorganisms that reside on the skin include viruses, bacteria, fungi and mites [1]. Figure 1 provides an example of the areas these microorganisms reside. Variation also occurs depending on human age and sex. Culturing systems have only gone so far, and more information has been obtained from 16S ribosomal RNA metagenomic sequencing. Samples can be extracted from bacterial communities in both environmental and clinical samples. Metagenomic Analysis In a metagenomic study conducted by Grice et al., 20 different skin sites were found to host particular bacterial communities in samples obtained from healthy humans. Furthermore, community complexity was dependent on the particular characteristics certain skin sites harbored. In this study, 112,283 close to full-length bacterial gene sequences were obtained from 20 different sites on the skin, collected from 10 different humans in a healthy state. A majority of the bacteria found from these samples could be placed in one of four different phyla. These phyla included Actinobacteria (51.8%),Firmicutes (24.4%), Proteobacteria (16.5%), and Bacteroidetes (6.3%) (Grice e t al., 2009). 62% of the sequences identified as one of the three following bateria: Corynebacteria, Propi'onibacteria'', or Staphylococci. Many of the 20 skin sites that were selected for this study were ones that have been associated with particular dermatologic disorders. Understanding the complex community in these particular sites is essential for understanding what changes during states of pathogenesis. ' Sites that were chosen include the following: in between the eyebrows, next to the nostril, inner ear, scalp, upper chest, nostril hair, armpit, elbow, in between fingers, side of groin, fold between the buttocks, back of knee, heel, belly button, mid forearm, palm of hand, and buttock [2 ]. These sites can be broken down into three types of environments: moist, dry, and sebaceous. ''Corynebacteria were mainly found in moist environments, as shown in Figure 2. '' Staphylococci species were also found in the moist environment skin sites. Dry skin sites had more of a mixed microbial population, with beta-Proteobacteria and Flavobacteriales species having the most presence, as shown in Figure 3. Sabaceous skin sites had prominent populations of ''Propionibacteria and Staphylococcus, as shown in Figure 4. The results of this study show an in-depth profile of many sites on the human skin, and demonstrate the differences in microbial communities based on the type of environment. References [1 Grice E and Segre J. The skin microbiome. Nature Reviews 2011(9) 244-253.] [2 Grice E, Kong H, Conlan S, Deming C, Davis J, Young A, NISC Comparative Sequencing Program, Bouffard G, Blakesley R, Murray P, Green E, Turner M, Segre J. Topographical and temporal diversity of the human skin microbiome. Science 2009 (324) 1190-1192.]